The present invention relates to hematopoietic stem cells and to methods of treating diseases and disorders, including genetic diseases and disorders and infectious diseases, using same. The invention additionally relates to methods of identifying agents that promote growth, engraftment or differentiation of stem cells.
The ability to isolate and manipulate hematopoietic stem cells (HSC) for the purposes of gene therapy and transplantation has drawn intensified interest in recent years (Emerson, Blood 87:3082 (1996); Karlsson, Blood 78:2481 (1991)). Functionally, the most primitive hematopoietic stem cells have extensive potential for self renewal and can give rise to all blood cell lineages. Currently, however, the phenotype of the most primitive human hematopoietic stem cells remains unclear. Primitive human hematopoietic progenitors with extensive potential for self renewal and multilineage development have been characterized by numerous groups using both in vitro assays and chimeric animal models. These studies suggest that the most primitive human HSC express the CD34 surface marker (CD34+), lack obvious lineage commitment markers (Linxe2x88x92) and express low to undetectable levels of other cell surface markers including CD38, CD71 CD45RA, and Thy-1 (Terstaypen et al, Blood 77:1218 (1991); Landsdorp et al, J. Exp. Med. 178:787 (1993); Cicuttini et al, Growth Factors 10:127 (1994); De Bruyn et al, Stem Cells 13:281 (1995); Di Giusto et al, Blood 84:421 (1994); Hao et al, Blood 86:374 (1995); Huang et al, Blood 83:1515 (1994); Muench et al, Blood 83:3170 (1994); Rusten et al, Blood 84:1473 (1994)). Despite this evidence, to date there have been no human transplant studies to formally determine the phenotype of the most primitive human hematopoietic stem cells.
Recently, three studies using long term murine bone marrow transplant models have indicated that there are populations of primitive HSC that express low to undetectable amounts of CD34 (CD34loxe2x88x92 cells) and that are capable of durably generating lymphoid and myeloid lineages following their transplantation. Osawa et al (Science 273:242 (1996)) demonstrated that a single Linxe2x88x92c-kit+Ly6A/Sca-1+CD34lo/xe2x88x92 cell could result in long term hematopoietic reconstitution in recipient mice. Jones et al (Blood 88:487 (1996)) identified a population of small Linxe2x88x92CD34lo/xe2x88x92AA4.1xe2x88x92 cells that expressed high levels of aldehyde dehydrogenase that were capable of durably generating lymphoid and myeloid lineages following engraftment. Morel et al (Blood 88:629a (1996)) demonstrated that Linxe2x88x92thy-1loLy6A/Sca-1+CD34lo/xe2x88x92 cells contain high proportions of long-term repopulating HSCs.
The present invention is based, at least in part, on the finding that human CD34xe2x88x92 HSC exist and that these cells, designed CD7+CD34xe2x88x92Linxe2x88x92 cells, possess properties consistent with primitive pluripotent cells.
The present invention relates to hematopoietic stem cells, designated CD7+CD34xe2x88x92Linxe2x88x92 cells. The invention further relates to methods of treating diseases and disorders using such cells. Examples of diseases that can be treated with the cells of the invention include both genetic and infectious diseases. The invention also relates to methods of identifying agents that can be used to promote growth and engraftment of stem cells, as well as the differentiation of such cells.
Objects and advantages of the present invention will be clear from the description that follows.